What primarily influences the permeability of a soil?

The permeability of soil is primarily influenced by the grain size and arrangement of pores within that soil. Grain size determines how water and air move through the soil: larger grains create larger spaces or pores, allowing water to flow more freely, whereas smaller grains fill in the spaces, restricting flow. Additionally, the spatial arrangement of these grains affects how interconnected the pore spaces are. When the pores are well-connected, water can easily travel through the soil. This relationship highlights that the physical characteristics of the soil at a granular level are key determinants of its ability to transmit water.

Other factors mentioned, such as soil organic matter content, relative humidity, and soil color, do play roles in soil function and properties but are not as directly impactful on permeability as grain size and pore arrangement. For instance, while organic matter can improve soil structure and enhance water retention, it does not directly dictate how quickly water can move through the soil compared to the physical arrangement of the grains.